Trunking arrangement for automatic or semiautomatic telephone systems



May 22, 1928. 1,670,420

J. E. OSTLINE ET AL TRUNKING ARRANGEMENT FOR AUTOMATIC OR SEMIAUTOMATIC TELEPHONE SYSTEMS Filed May' 9, 1925 am 59% Fassmure Patented May 22, 1928.

UNITED STATES PATENT OFFICE.

JOHN E. osTLINE AND I LIAM o. PAssMoEE, OF LIVERPOOL, ENGLAND, ASSIGNOBS, BY MESNE ASSIGNMENTS, T A TOMATIC ELECTRIC mm OF CHICAGO, ILLINOIS,

A CORPORATION or DELAWARE.

TEUNKING ARRANGEMENT FOR AUTOMATIC OR sE'MIAUToMATrC TELEPHONE I SYSTEMS.

Application filed Kay 9, 1925, Serial No. 29,018, and in Great Britain July 17, 1924.

The present invention relates to improved trunking arrangements foruse in automatic or semi-automatic telephone systems, particularly to those which afi'ord what are known as private branch exchange facilities in which a number of lines leading to the same subscriber are all reached from a calling automatic subscriber by dialling the same number. The general arrangement is somewhat similar to that disclosed in copending application Serial No. 8,271 filed February 10, 1925, but has been modified to obtain greater economy particularly in the case of a group of from 20400 lines.

According to one feature of the invention in a telephone system including private branch exchanges, hunting switches are employed, for selecting an idle .lineleading to a private exchange and battery feed and supervisoryarrangements for such a line are associated with the hunting switches.

According to another feature of the invention in a telephone system employing hunting switches for obtaining access to private branch exchange lines, a number of hunting switches 'eachhaving access to a different group of lines leading to a private branch exchange are arranged to form a unit with a single set of battery feed and supervisory apparatus. p

A further feature of the invention is the provision of a telephone system in which access is obtained by means of a plurality of hunting switches to agroup of lines greater in number than the capacity of an individual switch, the switches forminga unit and being arranged to hunt successively. The hunting switches employed are preferably homing type rotary switches and are provided with two sets of wipers and corresponding bank contacts. The contact banks are semi-cylindrical and similarly situated while thesets of wipers are diametrically opposed to one another so that when one set is engaging itsbank contacts the other set is disconnected. This arrange ment enables sets of contacts to be obtained by using a 25 point switch of knowntype.

The above mentioned features and others not specifically mentioned at this point will 50 be better understood from the following descrlption of a preferred form of the invention. It will be understood, however, that this isby way of example only and that considerablemodifications could be made in 5 the circuit details without exceeding the scope of the invention.

Referring now to the accompanying drawings Fig. 1 is a layout diagram showing the general trunking arrangements, while Fig. 2 is a detailed circuit diagramof the apparatus accessible from the bank of the second selector.

Suppose that in Fig. l the subscriber A wishes to converse with a subscriber of the private branch exchange towhich the lines X lead. It is assumed in the example shown that the number of lines is between 50 and 100 so that two hunting switches coupled together will be provided. The connection 7 then extends over the subscribers line switch C, the first selector D and the second selector E to the repeater B. This repeater contains the usual ringing, supervisory and battery feed arrangements and has asso- 15 ciated with it the pair of rotary line switches L and L which are of the homing type and are arranged to work in conjunction.

The arrangements are such that L is always taken into use first and hunts to find a free line. The fiftieth contact of switch L has no trunk line connected to it and if the switch is advanced to this position without finding a free line armature T is i changed over and switch L takes up the hunting operation and when it finds a free line the connection is completed thereover. In case line switch L also fails to find a free line, and in the limiting case reaches its fiftieth position, arrangementsare provided for giving the subscriber the busy. signal. Both switches are restored to normal when the calling party hangs up,

whether at the end of the conversation or on receiving the busy signal.

Outgoing connections from the private branch exchange are completed over primary line switches such as LS and LS and during an outgoing call, the test contact in the bank of switches L or L associated with the line in use is marked busy so that this line shall not be taken into use for an incoming call. All of the lines X may be equipped both for outgoing and incoming calls, or some may be devoted exclusively to trallic in one particular direction, in which case they will of course, be employed in preference to lines equipped for both way working. The actual division will depend on the nature of the traiiic; for instance, in the case shown if the incoming trallic normally preponderated the lines extending from L might be used for incoming trailic only while those from I) were used for tratfic in both directions.

The switches such as LS may be provided with the known mechanical interlocking relays or a normal position may be used in which the switch remains for incoming calls. Lines may be connected to all the contacts oi switch L except the last, or if itis considered that this involves risk of sinniltaneous seizure of the first line by two second selectors, the first set of contacts may be left blank.

It should be pointed out that when an ordinary subscriber is called, the last two digits of the number dialled operate a connector and in the case of small private branch exchanges operate a rotary connector. In the case. however, of large P. B. X.s to which access is obtained direct from a selector level as in the arrangement according to the invention only one digit is required and if the numbering scheme is to be kept uniform the remaining digit will have to be absorbed. It is preferable that this digit should not be dialled on the wanted partys line and it is, therefore, provided in the arrangement about to be described that the operation of the hunting switches does not take place until the receipt of the first impulse of the extra train. Consequently the series of impulses and the hunting movement may be considered as occurring at substantially the same instant and the extra digit is absorbed in the relay group associated with the hunting switches.

Referring now to Fig. 2, the setting up of a connection will be traced through in detail. 1, 2 and 3 represent contacts in a certain level-as shown in Fig. 1 the seventhof a. second selector which are assumed to have been connected with by the subscriber A. When the selector switches through on the termination of the hunting operation, a circuit is completed over the subscribers loop and the normally closed springs controlled by armatures 5 and 6 for line relay 4 which thereupon energizes and operates armature 7. A circuit is now completed for slow release relay 8 which upon energizing at armature 9 connects earth to the release trunk conductor 10, at armature 11 opens the homing circuit of switch L, at armature 12 prepares a circuit over armature and its back contact for relay 13, and at armature 12 prepares a locking circuit for relays 13, 17 and 31. No further circuit changes take place until the calling party dials again whereupon a circuit is completed for relay 13 over armature 7 and its ack contact, armature 12 and its front contact and armature 20 and its back contact. Relay 13 thereupon energizes and at armature 14 opens a point in the ringing circuit, at armature 15 completes a locking circuit for itself, at armature 16 completes a circuit for test relay l7 and rotary magnet 22 in series and at armature 15 connects test wiper 23 to the junction of relay 17 and magnet 22 by way of back contact and armature 19 and normally closed springs controlled by armature 43. Relay 13 moreover at armature '16 alters the connections of the busying circuit for a purpose which will be described subsequently. In case the first line connected to the home position of switch L is free, relay l7 switches through at once and ringing starts. Suppose however that a number of the first choice lines are busy, earth will be present on the test contact 24 with which wiper 23 is in engagement, relay 17 will be short circuited and magnet 22 will be operated to advance the wipers one step. As the next line is busy also, the same operation is repeated and the hunting operation continues until test wiper 23 engages a contact which is not earthed: suppose that contact 25 is the first one found. Relay 17 now energizes in series with magnet 22, the latter not now being operated. ltelay 17 at armatures 20 and 20 opens the circuit of relay 13 at the same time completing a locking circuit for itself, at armature 19 connects earth to test wiper 23 and at armatures 18 and 20 connects the speaking leads through. The ringing circuit is now completed as soon as relay 13 de-energizes and extends from battery, back contact and armature 34, armature 21 and its front contact, armature and its back contact, wiper 47, contact 27.v lead 29 to the P. B. X., lead 28, contact 26, wiper 46, back contact and armature 48, front contact and armature 18, armature 32 and its back contact, back contact and armature 14, back contact and armature 38, upper winding of ringing trip relay 31 to the ringing generator GEN. A certain amount of ringing current leaks back by way of the small condenser 49 so as to give the calling subscriber ringing induction. When the call is answered by the P. B. X. operator, a direct current loop is completed across leads 28 and 29 and the ringing trip relay 31 is operated. Relay 31 upon operating, at armature 33 completes a locking circuit for itself and at armatures 32 and 34 stops the ringing and connects the speaking leads through. A circuit is now completed for back bridge relay 35 which upon energizing, at armatures 5 and 6 reverses the current flow back over the con nection for metering or analogouspurposes. Conversation may no-wtake place as desired, and when it is finished, the calling party will replace his receiver. When this occurs, the circuit for line relay 4 is opened and it de-energizes, thereby at armature 7 opening the circuit of relay 8. The latter therefore de-cnergizes also after an interval and at armature 9 removes earth from release trunk conductor 10 so as to release the receding switches. Moreover at armature 12 the locking circuit for relays 17 and 31 is opened so that they de-energize while at armature 11 the circuit is completed for restoring the switch L to normal. This circuit extends as follows: battery, magnet 22 and its interrupter contact, back contact and armature 42, armature 11 and its back contact, homing wiper 51, to earth by way of the multipled contacts in its bank. The switch wipers are thus restored to normal position whereupon wiper 51 engages a dead contact and no further motion takes place. All the apparatus has now been restored to normal and the repeating apparatus and also the particular line employed may be used for completing other connections.

The case will now be considered in which no lines leading from the switch L are idle so that it is necessary for the connection to be completed over the switch L The seizure of the repeater and the initial hunting operation takes place as previously described and the wipers of the switch'L are advanced into engagement with the last set of contacts in their respective banks. A circuit is now completed over wiper 23 and contact 50 for the magnet 22 and the lower winding of relay 4L0 in series. The resistance of the lower winding of relay 40 however is so chosen that it is low enough to shunt relay 1 7 sufiiciently to preventit operating and yet sufficiently high to prevent magnet 22 operating in series with it. Consequently, only relay 40 now operates; at armature 4d locks itself up to the release trunk conductor through its upper winding, at armatures 48, 43 and 45 disconnects the wipers of switch L and connects up those of switch L at armature i1 opens the homing circuit and at armature 42 connects magnet 46 to the test circuit. Switch L now commences to hunt in known manner under the control of test wiper 52, and when it finds a free line the connection is completed in the manner just described.

lVhenthe conversation is finished, the calling subscriber replaces his receiver and theconnection is released in the manner previously described. It will be'noted that relay 40 is released when earth is removed.

whereupon wiper 52 engages contact 54 to which no earth is connected. Hence relay 17 isno lon 'er short circuited and o crates thereby at armature 19 connecting earthto wiper 52.. A circuit now completed for busy relay 3? which upon operating, at armature 38 opens a point in the ringing circuit, at armature 39 completes a locking circuit for itself at the same time opening the circuit of relay li so that this relay deenergizes and at armature 39 removes the short circuit around resistance 36 and connects up busy tone and busy flash battery by way of the lead BF. The calling subscriber thus i'iotilicd that he cannot obtain his connection and accordinglyhangs up his receiver, whereupon the connection is released in the manner previously described. The busy [lash' battery is, as is well known, only usefully operative in case the connection has been set up by an operator, in which case it causes the supervisorylamp to flash.

The additional armature 16 on relay 13 becomes usefully operative under the following ('lI'CUIDStZIHCGS. Suppose that "for some reason the calling party should operate his impulse senderwhile the busy signal is being transmitted to him; it might happen that owing to the resistance 36 included in its circuit, the time of de-energization of relay i might be so increased that relay 8 would fail to hold up. The whole connection would then be released and the calling subscriber not hearing the busy signal would be at a loss to understand what had occurred. \Vitlr the present arrangement, however, if the subscriber dials again,isince relay 17 has released, a circuit is completed for relay 13. Relay 13 upon energizing, at armature 16" cuts oil the busy flash battery and again shortcircuits the resistance 36; hence relay i receives its normal flow of current and there is no danger of the connection being prematurely released.

It should be mentioned that though the employment of two switches which hunt successively has been described, in case the P. B. X. lines numbered less than only one switch such as L would be required, In this ace, the busy relay instead of the change over relay would be connected up to the last contact or" the switch.

hat is claimed is:

1. Ina telephone system, a group of nonnumerical trunk hunting switches, trunk lines accessible in the banks of each switch, means for operating one of said switches for connecting a callin and a called station, and means indivi nail to said group of switches for supplying current to the calling line.

2. In a telephone system, a group of nonnumerical trunk hunting switches, trunk lines accessible in the banks of each switch, means for operating one of said switches for connecting a calling and a called station, and means individual to said group of switches for supplying current to the called line.

3. In a telephone system, a group of nonnumerical trunk hunting switches, trunk lines accessible in the banks of each switch, means for operating one of said switches for connecting a calling and a called station, and means individual to said group of switches for signalling the called subscriber.

4. In a telephone system, a group of nonnumerical trunk hunting switches, trunk lines accessible in the banks of each switch, means for operating one of said witches for connecting a calling and a called station, and means individual to said group of switches for testing said trunk lines.

5. In a telephone system, a group of nonnumerical trunk hunting switches, trunk lines accessible in the banks of each switch, means for operating one of said switches for connecting a calling and a called station, and means individual to said group of switches operative when the called party responds for reversing the normal current flow over the calling line.

6. In a telephone system, a switching device comprising a plurality of non-numerical hunting switches, each switch having a set of wipers and a stepping magnet, a separate group of trunk lines accessible to each switch, means for successively operating said switches until one switch finds an idle trunk for connecting a calling and a called Ftation, and means individual to said switching device for signalling the called subscriber.

7. In a telephone system, a switching device comprising a plurality of non-numerical hunting switches, each switch having a set of wipers and a stepping magnet, a separate group of trunk lines acces-ible to each switch, means for successively operating said switches until one switch iinds an idle trunk for connecting a calling and a called station, and means individual to said switching device for testing the lines in each group.

8. In a telephone system, a switching device comprising a plurality of non-numerical hunting switches, each switch having a set of wipers and a stepping magnet, a separate group of trunk lines accessible to each switch, means for successively operating said switches until one switch finds an idle trunk for connecting a calling and a called station, and means individual to said switching device for supplying current to the calle line.

9. In a telephone system, a switching device comprising a plurality of non-numerical hunting switches, each switch having a of wipers and a stepping magnet, a separate group of trunk lines accessible to each switch, means for successively operating said switches until one switch linds an idle trunk for connecting a calling and :1 called station, and means individual to said switching device for supplying current to the calling line.

10. In a telephone system, a switching device comprising a plurality of nonnuinerical hunting switches. each switch having a set of wipers and a stepping n'iagnet, a separate group of trunk lines accessible to each switch, means for successively operating said switches until one switch finds an idle trunk for connecting a calling and a called sta' tion, and means individual to said switchiug device for reversing the normal current tiow over the calling line responsive to the response of the called party.

1]. In a telephone system, a trunk line, a plurality of trunk hunting switches terminating said trunk line, each switch having access to a different group of trunk lines, and means responsive to a call received over said trunk line for operating one or more of said hunting switches to ex tend the call, the number of switches operated depending on the busy or idle condition of the trunk lines accessible to said switches.

12. In a telephone system, a non-numerical hunting switch, a trunk line terminating in said switch, means operated responsive to a digit of a particular value diallcd by a calling subscriber for extending a connection to said trunk line, and means responsive to another digit of any value dialled by such subscriber for starting the operation of said hunting switch.

13. In a telephone system, two non-numerical trunk hunting switches, a numerical switch, means controlled by a calling subscriber for operating said numerical switch to connect with said non-numerical switches via a trunk line, means controlled by the calling subscriber at; will for starting the hunting movement of the first of said nonnumerical switches, and means controlled by a particular operation of the first of said non-numerical switches for starting the hunting movement of the second of said nonnumerical switches.

14. In a telephone system, a first and a second non-numerical trunk hunting switch, each switxrh having a set of wipers and a motor magnet, a separate group of trunks Hill accessible to each switch and extending to a the same point, means common to said switches for testing trunk lines, means controlled by a calling subscriber for starting said first switch to hunt an idle trunk,and means operative when all the trunks accessible in the banks of said first switch are busy for starting said second switch to hunt an idle trunk.

15. Ina telephone system, a first and a second non-numerical trunk hunting switch, each switch having a set of wipers and a motor magnet, a separate group of trunks accessible to each switch and extending to the same point, means common to said switches for testing trunk lines, means con trolled by a calling subscriber forstarting said first switch to hunt an idle trunk, means operative when all the trunks accessible in the banks of said first switch are busy for starting said second switch to hunt an idle trunk, and means effective in case all the trunks accessible in the banks of said second switch are busy for giving the called subscriber a busy signal.

16. In a telephone system, a main exchange, a branch exchange, a trunk line connecting said exchanges, means including an automatic hunting switch in the main exchange for extending a calling line to said trunk line, a trunk line terminating in said switch, a repeater in the main exchange included in said second trunk line, and means in said repeater responsive when the said first trunk line is seized for transmitting signalling current over said first trunk line to the branch exchange.

17. In a te'lephone system, a trunk hunt ing switch, trunk lines accessible to said switch, means controlled by a calling subscriber for operating said switch to hunt an idle trunk, means operable when saidswitch finds all of said trunk lines busy for inserting a resistance in the calling line, and means controlled by the calling subscriber for short cireuiting said resistance.

18. In an automatic telephone system, a

trunk hunting switch for extending connections between calling and called stations, trunk'lin'es accessible to said switch, means for operating said switch to hunt an idle trunk, means operable when said switch finds all of said trunk lines busy for signalling the calling subscriber, and means operative providing the calling subscriber actuates the dial at the calling station after said i switch is operated for temporarily interrupting said signal while the dial 1s being actuated. V

19. In a telephone system, a group of trunks, means for extending connections from calling lines to idle trunks of said group, a sub-group of non-numerical hunting switches terminating each trunk of said group, called lines'acce-ssible to said switches,

and means individual to each subgroup of switches for supplying current to a calling line. I g

20. In a telephone system, a group of trunks, means for extending connections from calling lines to idle trunks of said group, a "sub-group of non-numerical hunting switches terminating each trunk of said.

group, called lines accessible to said switches,

and means individual to each subgroup of switches for supplying current toa con nected called line.

21. In a, telephone system, a group of trunks, means for extending connections from calling lines to idle trunks of said group, a sub-group of non-numerical hunting switches terminating each trunk of said group, called lines accessible to said switches, and means individual to each sub-group of switches for signalling over a connected called line. I

22. In a telephone system, a group of trunks, means for extending connections from calling lines to idle trunk-s of said group, a sub-group of non-numerical hunting switches terminating each trunk of said group, called lines accessible to said switches. and means individual to each sub-group of switches for reversing the normal current flow over a calling line.

23. A switching devlce comprising two I permanently paired rotary line switches for use alternatively in extending connections from a calling line to called lines, and means included in said device for supplying current to the calling line.

24. A switching device comprising two permanently paired rotaryline switches for use alternatively in extending connections from a calling line to called lines, and means included in said device for supplying current to a called line.

25. A switching device comprising two permanently paired rotary line switches for use alternatively in extending connections from a calling line to called lines, and means included in said device for signalling over it called line.

26; A switching device comprising two permanently pairedrotary line switches for use alternatively in extending connections from a calling line to called lines, and means included in said device for testing the called 1 lines.

27. A switching device comprising two permanently paired rotary line switches tor use alternatively in extending connections from a calling line to called lines, and means included in said device for reversing the normal current flow over the calling line.

28. In a telephone system, a plurality of hunting switches, trunks accessible to each switch, and-means for successively operatoperated switches to normal in the reverse 1 order in which they are operated.

In witness whereof, I hereunto subscribe my name this 21st day of April. A. D. 1925.

JOHN E. OSTLINF. In witness whereof, I hereunto subscribe 15 my name this 21st (lay of April, A. I). 1925.

WILLIAM O. PASSMURI'J. 

